1. Field of the Invention
The present invention relates to a motion transmission apparatus, and more particularly to a chain for a motion transmission apparatus.
2. Description of the Prior Art
Currently a type of motion transmission apparatus with a chain has been invented to reduce the noise of the motion transmission apparatus and the friction between the rolling elements, wherein the rolling elements are received in the chain so that they can be prevented from impacting one another, thus reducing the generation of noise. Furthermore, the rolling elements are prevented from contacting each other so that the friction between the rolling elements is also reduced, which, as a result, extends the service life while ensuring a precise and smooth operation of the chain.
Although the transmission apparatus with a chain has a lot of advantages, it might stop the rolling elements from moving smoothly while reducing the precision of the rolling elements' motion and causing severe damage if the structural design of the chain is not in line with the motion track of the motion transmission apparatus. For example, U.S. Pat. No. 5,993,064 discloses a chain structure which has two cross-shaped structures at both ends thereof and is provided with two strings of serially-connected and crosswise arranged rings. This chain structure is in arc-shaped line contact with the rolling elements, and it is impossible for the chain to be turned or twisted when the motion transmission apparatus is moving along its complicated motion track because these rings will be subjected to pressure and tensile deformation and cause interference with the inner surface of the motion track, which is likely to cause rupture of the chain and bad circulation of the rolling elements. Another conventional chain structure is disclosed in JP Pat. No. 2607993 and comprises a plurality of spacers connected by two links. Both sides of each spacer are defined with a concave (also called retaining surface) which is in arc-shaped line contact with the rolling elements. When the chain structure moves along the twisted or curved endless circulation path, the concave of the spacers is unable to keep in full contact with the rolling elements. Furthermore, when moving through a curved path, the deformation of the chain will make the spacers shift toward the inner side of the curved path, as a result, the spacers will rub against the inner surface of the path, causing friction, which will further result in a bad circulation of the rolling elements.
The present invention has arisen to mitigate and/or obviate the afore-described disadvantages.